A large species (attaining more than 50 kg). The systematics of this species is currently under review and it will probably be placed in the unique genus Spiniraja (Peter Last, CSIRO Hobart, pers. comm.).

Justification:
The Melbourne Skate (Dipturus whitleyi) is an Australian endemic, found on the continental shelf between Wollongong (New South Wales) and Albany (Western Australia) and Tasmania. This large skate species (to 201 cm TL) is vulnerable to fishing pressure due to its large size at birth and late maturity. It is benthic, found at depths of 0–170 m. Tending to be patchy in distribution, large individuals could be solitary. The species is relatively rare in outlying areas of Western Australia and northern New South Wales and probably has a narrow home range. It occurs inshore and is highly accessible and vulnerable to fishing pressure from gill nets through most parts of its range. It is likely to follow the trend of other large skates, which have declined in numbers. There is a strong basis for inferring that sustained trawling over 20 years is the predominant and most likely cause of the observed changes in relative abundance of rays, including D. whitleyi on the New South Wales upper continental slope. Observer data also provides some evidence that this species has declined. Despite this, its presence in shallow waters also affords it refuge from fishing pressure. It may be more abundant in shallow water, for example it is frequently captured in inshore waters off Hobart. Given observed declines, combined with areas of refuge, this species is assessed as Vulnerable, based on continuing overall declines of >30%.

Widely distributed throughout southern Australia on the continental shelf, often in the coastal zone from Wollongong (New South Wales) to Albany (Western Australia) including Tasmania (Last and Stevens 1994).

Countries occurrence:

Native:

Australia (New South Wales, South Australia, Tasmania, Western Australia)

Populations are patchily distributed around southeast Australia. The species is relatively rare in outlying areas of Western Australia and northern New South Wales; it probably has a narrow home range making it vulnerable to localised fishing (Peter Last, CSIRO Hobart, pers. comm.).

Fishery independent surveys off southern New South Wales have shown that catch rates have declined by 83% between 1976/1977 and 1996/1997 for grouped “skates” (Graham et al. 1997, Graham et al. 2001). A survey was carried out from 1976–1977 on the upper continental to 275 m off Ulladulla and Eden mainly comprised Dipturus australis, Dipturus sp. A and D. whitleyi. In 1996–1997 the survey was repeated in the same area and showed that numbers of all skates had depleted. Off Ulladulla the mean catch rate for all species at all depth zones in 1976–1977 was 32.6 kg per hour and in 1996 to 1997, 3.9 kg per hour. Off Eden the mean catch for all species at all depth zones 1976–1977 was 32.4 kg per hour and in 1996–1997, 5.0 kg per hour (Graham et al. 2001).

Despite several years of searching for pregnant females around Tasmania and in the southeast non-trawl and trawl fishery, only one individual with egg cases was found by a local fishermen in 5 m of water (Treloar unpubl. data).

It is one of few hard bottom dwelling skates occurring on reef but is also found on soft bottoms from depths of 0–170 m. Soft ground habitat, such as sand, mud and gravel is considered to be at moderately high risk from trawling activities (New South Wales Department of Primary Industries 2004).

There may be habitat partitioning between juveniles and adults. Large individuals are often seen on rocky substrates (Peter Last, CSIRO Hobart, pers. comm.). Despite several years of searching for pregnant females around Tasmania and in the southeast non-trawl and trawl fishery, only one individual with egg cases was found by a local fishermen in 5 m of water (Treloar unpubl. data).

Young and sub-adults are caught as bycatch in the Commonwealth Trawl Sector of the Southern and eastern Scalefish and Shark fishery. This species is harvested, with 16–55% of the 2002–2005 D. whitleyi catch in the Commonwealth Trawl Sector being retained (Treloar unpub. data). There is a strong basis for inferring that sustained trawling over 20 years is the predominant and most likely cause of the observed changes in relative abundance of rays on the New South Wales upper continental slope (Graham et al. 2001). Large individuals are most vulnerable to hook and line, but also to gill nets. In 2004, 31% of licences in the Tasmanian State fisheries were in the scale-fish fishery (netting and hooks). There are no trawlers in Tasmanian State waters; these consist of gill netters and hook and line fishers (ABARE 2005).

Based on observer data, standardized CPUE in the Southeast Fishery increased from 1992–1995, showed a decline from 1995–1998, then remained stable from 1998–2002 (Terry Walker, PIRVE, unpublished data). Despite this, the species presence in shallow waters also affords it refuge from fishing pressure. It may be more abundant in shallow water, for example it is frequently captured in inshore waters off Hobart (J. Stevens pers. comm. 2007).

Recommendation: better contemporary data of population size and distribution to evaluate the need to implement management practices. This may need to be done as a matter of urgency to avoid further depletion.

Australian Bureau of Agriculture and Resource Economics. 2005. Australian Fisheries Statistics 2004. Canberra.

Graham, K.J., Andrew, N.L. and Hodgson, K.E. 2001. Changes in the relative abundances of sharks and rays on Australian South East Fishery trawl grounds after twenty years of fishing. Journal of Marine and Freshwater Research 52: 549‒561.